Various processes are presently being utilized for forming seamless containers from flat metal blanks. One well known common commercial procedure involves first forming a circular metal blank from an aluminum, steel or other metal stock sheet. Subsequently, in what is commonly referred to as a cup make machine, the metal blank is formed into a shallow cup by forcing the blank through a drawing die by means of a punch mounted on a press. Such cups are then fed into a body maker apparatus wherein a reciprocating ram with a punch attached to the forward end thereof engages one of the cups and forces such cup through a die assembly having one or more dies to form an elongated seamless container body. The body maker dies may first include a redraw die which reforms the cup into a cup of smaller diameter and longer sidewalls and then a series of ironing dies having inside diameters which are progressly slightly smaller than the outside diameter of the cup. These ironing dies elongate the sidewall of the redrawn cup by reducing its thickness without reducing the inside diameter of the cup to produce a thin walled container body. The thickness of the bottom wall of the container remains unaltered to provide desired structural requirements which are greater in the container bottom wall area than in the sidewall for containers filled with pressurized contents, such as beer and carbonated beverages. After forming the container sidewalls the bottom wall is usually formed to a domed configuration to further increase its pressure resistance capabilities. Thus by forming the container body with thinner ironed sidewalls the container body can meet desired structural requirements yet be formed utilizing less metal stock material than if such container body did not have reduced thickness sidewalls.
Since all body makers produce container bodies having some inconsistency in the length of the sidewall the ironed container body sidewall is then trimmed to a predetermined constant length and thereafter the open end is necked-in and provided with a flange for seaming thereto a closure end to seal the container after filling. For greater detail regarding the production of seamless metal containers, reference is made to an article appearing in the November, 1973 issue of Aerosol Age Magazine, entitled "The Drawn and Ironed Can Understanding the Technology."
In order to reduce production cost of the container bodies attention has been given to increasing the production speed of the bodymaker ram and also to reducing the amount of starting metal stock material required for forming the container body. One typical early metal two-piece can bodymaker to which this invention relates includes a horizontally reciprocating ram which at the forward end is movably supported and aligned in its stroke by a stationary forward hydrostatic oil bearing sleeve circumferentially surrounding the ram and secured to the body maker. The other, or rearward, end the ram is supported by an hydrostatic oil bearing slide block assembly which includes means for connecting the ram to the body maker drive mechanism. The slide block assembly constantly moves backward and forward with the rearward end of the ram during its stroke providing support and aligment therefore.
One limitation on the ram speed capabilities of such prior art body makers is that the hydrostatic oil bearing slide block assembly must be relatively massive, typically weighing approximately 240 lbs, to provide the desired support and alignment of the rearward end of the ram during its stroke. With this mass reciprocating at over 200 times per minute and with the distance between the two supporting points constantly changing, and with the tremendous forces generated in the high speed redrawing and ironing of the container body, it can be appreciated that the support and alignment of the container body maker ram is a complex problem.
One proposed design for increasing the speed of the reciprocating ram for a given power output and hence container production, is shown in U.S. Pat. No. 4,173,138. That reference discloses supporting the ram with two stationary axially-spaced hydrostatic oil bearing sleeves rather than the single oil bearing sleeve utilized in the earlier prior art body maker discussed above, however it teaches that the purpose of utilizing the two stationary oil bearing sleeves to align the ram is to allow the connection between the slide block and the rear end of the ram to be of a flexible nature so that the ram is isolated from the slideblock regarding non-axial movement. Thus the drive mechanism is only required to transmit forward and rearward motion to the ram, and not be relagated to a function of critically alignment of the ram since an alignment function would act to reduce the axial rearward and forward power transmitted to the ram thereby reducing ram speed.
In addition to providing flexibility in the connection, between the ram and slide block assembly, U.S. Pat. No. 4,173,138 also teaches that the slide block assembly itself can be provided with lateral flexibility or play relative to the slideway within which the slide block assembly is mounted. Utilization of such an arrangement is said to further isolate the rear end of the ram from an alignment function ensuring that the forces of the drive mechanism are only utilized to transmit forward and rearward movement.
In practice we have discovered the flexible or loose connection between the rearward end of the ram and slide block assembly cannot provide critical alignment and hence misalignment of the ram occurs. Loss of critical alignment is undersireable since it manifests itself by the production of out of spec container bodies having overly inconsistent sidewall length and thickness.
To a certain extent all body makers produce container bodies having portions of the sidewall which are of a greater or lesser length from the bottom wall to the open end than other regions of the sidewall and thus, as discussed above, it is required that the container bodies be trimmed in a separate operation to a constant standard length. The trimmed container bodies allow standardization of their length and volume and provide an edge at their open end which can readily be adapted for receiving a closure end. The amount of metal trimmed from the container body however represents metal scrap, and therefore it can be appreciated that the more consistently uniform the length of the sidewall is, the less metal need be used and less scrap need be produced. Thus it is desirable that consistent side wall length occur during container body formation, such undersirable inconsistency in sidewall length is commonly referred to as "earing" or "sugar scooping."The term "earing" represents container bodies having localized sidewall regions of greater length than adjacent regions wherein the longer sidewall regions appear as somewhat ear-like shaped pieces of metal extending about the open edge of the sidewall. "Sugar scooping" refers to container bodies wherein one side of the container body is of a noticable longer length then the other side, somewhat akin to the shape of a sugar scooper. Container bodies formed with excessive earing and sugar scooping also presents problems in the flanging of the container bodies. This is because such containers have non-uniform sidewall thicknesses in the region adjacent to the open end of the container and thus, during the operation of forming the flange on the container body, a splitting of the sidewall at the flange is much more likely to occur. Earing and sugar scooping, as well as less severe inconsistences in the length of the container sidewall, most often are the result of ram misalignment relative to the bodymaker die assembly.
U.S. Pat. No. 4,173,138 teaches that the flexibility and play in the ram to slide block assembly connection has its greatest effect on misalignment when the ram is at the end of the rearward stroke since at this time the distance between rear end of the ram and the aligning stationary oil bearing sleeves is greatest. According to the reference, the need for critical alignment is not great at this time since the ram is not in a functioning part of its stroke relative to the die assembly. However in practice it has been found that ram alignment is indeed critical prior to the ram's entrance into operative relationship with the die assembly. This is because if the rear end of the ram is allowed to "fishtail" causing the front end of the ram to enter the die assembly in a misaligned manner, container bodies of overly inconsistent length and thickness can be produced. More specifically, where the first die of the die assembly is a redraw die the initial misalignment reforms the cup into a cup having sidewalls with a non-symetrical metal distribution which can eventually result in ironing to inconsistent container body sidewall lengths and thickneses, even if the remainder of the ram stroke is aligned relative to the ironing dies. As mentioned previously some body maker die assemblies do not include a redraw die. In such case the failure to provide critical alignment of the rear end of the ram as it initiates its stroke causes an inconsistent sidewall length since misalignment of the ram results in inconsistent ironing of the sidewall forming certain regions of the sidewall to greater or lesser length and thickness than other regions. Of course it is understood that any misalignment of the ram which continues past the initial die of the die assembly further compounds the problem of attempting to produce containers of relative consistent length.
In order to reduce container production costs to provide an advantage, manufacturers are continually striving to reduce the amount of metal utilized in forming a container body. Most commonly this is accomplished by maintaning the standard diameter of the disc blank stock but reducing its thickness, to for example 0.0145 inch thick H-19 temper aluminum stock. When using such thinner metal, ram alignment becomes even more critical since the container body is ironed to a length which is closer to the trim length than in the case where a thicker gauge stock is used and the container body is formed having a side wall more in excess of the trim length. Thus in utilizing the thinner guage metal it is more likely that ram misalignment causing earing or sugar scooping will result in a sidewall which fails in all regions to meet the minimum trim length. Moreover with the thinner gauge stock, inconsistent ironning resulting from ram misalignment is also more likely to result in sidewalls which do not meet minimum thickness requirements.
We have also found that the failure to provide critical alignment of the rear end of the ram as taught by the reference patent makes it less suitable for forming container bodies from the thinner gauge stock material where ram alignment is especially critical. Moreover the play provided by the flexible nature of the connection between the ram and slide block assembly allows more drift in the rear end of the ram. Such drift allows a leveraging of the tremendous forces generated during ironing and over a period of operating time has a tendency to cause serious misalignment of the ram. To correct such misalignment production must be halted, typically 6 to 8 hours, and valuable production time is lost during such shut down.